In a wavelength division multiplexing (WDM) passive optical network (PON), total network transmission capacity can be easily enhanced using a plurality of channels in which optical signals have different wavelengths. The wavelengths of signals that are transmitted and received in most current WDM-PON systems are fixed, and thus optical transceivers having different wavelengths are basically required to increase the number of channels. That is, 40 optical transceivers having different output wavelengths are required to transmit signals of 40 channels. In this case, since 40 optical transceivers having different wavelengths must always be provided in preparation for malfunctions of the optical transceivers, operation comes with financial burden.
To solve this problem, seed light injection-type WDM-PONs using a wavelength-independent optical transceiver that operates regardless of wavelength have been developed. The wavelength-independent optical transceiver has an advantage in that wavelength can be readily determined according to the wavelength of seed light since the optical transceiver can produce an output optical signal having the same wavelength as the injected seed light. Therefore, the wavelength-independent optical transceiver can be easily replaced when it malfunctions, and it is more economical since it is not necessary to have a spare optical transceiver on hand for every channel.
Wavelength-independent WDM-PON (i.e., colorless WDM-PON) technology satisfying these requirements has been widely studied all over the world. Also, among various techniques undergoing research, one technique that has been developed to the point of being put into use currently is wavelength locking type WDM technology that determines output wavelengths of a wavelength-independent light source using an incoherent broadband light source as a seed light source.